The present invention relates to an optimized power supply system for an electronic circuit.
A system of this type is already known, e.g. from Patent Document U.S. Pat. No. 5,218,705. The electronic circuit in question is contained in receiver apparatus for receiving personal messages and commonly referred to as a xe2x80x9cpagerxe2x80x9d. The power supply voltage for the electronic circuits of the pager is delivered via a variable-voltage DC-to-DC voltage converter from a rechargeable battery or from a non-rechargeable battery. To save energy, and therefore to increase the operating time of the pager between battery recharging or battery replacement, or to reduce battery costs, the power supply voltage is adjusted to an operating value. The operating value is determined on initializing operation of the pager, by taking into account the data rate at which the pager is to receive data, and it cannot be less than a minimum operating voltage. The minimum operating voltage is also determined on initializing operation of the pager, by means of tests during which the voltage is gradually reduced for as long as the electronic circuits operate correctly, then the lowest voltage defined in this way is memorized, and operation of the voltage converter is adjusted accordingly.
The power supply voltage is thus determined on the basis of tests which take place when the terminal is switched on. The setting is then not modified again until the apparatus is switched off.
Naturally, the same provisions can be applied to any portable apparatus that contains an electronic circuit and a power supply therefor based on a rechargeable battery or on a non-rechargeable battery, in order to increase the operating time between battery recharging or battery replacement, or in order to use a source that is of smaller capacity, and therefore of lower cost. However, in general, such provisions can be applied particularly advantageously to portable communications apparatus.
The invention is based on the observation that that type of apparatus is often switched on by its user when in a vehicle or when at home and on the point of leaving home. It then remains in operation while the user is away from home, which is when it is of use to enable the user to be reached, or to enable the user to communicate, while being distant from any fixed installation. Unfortunately, the conditions surrounding the apparatus can change considerably from the time at which it is switched on to the time at which it is actually used.
For example, in winter, from being initially in a room heated to 20xc2x0 C., the apparatus can then find itself in the open air at xe2x88x9210xc2x0 C. The cooling of the electronic circuits can slow down their operating rate, depending on the technology used, in the same way as it is slowed down by a reduction in its power supply voltage. Thus, under such conditions, if the power supply voltage of the pager really were at its minimum value, such a drop in the temperature of the apparatus could make it incapable of receiving a message correctly. Using the known system thus requires margins to be provided in order to cope with changing environmental conditions. Consequently, the power supply voltage setting is not genuinely optimum.
It is also possible to consider the opposite case, i.e. in summer, with the apparatus initially in a cool room, and then taken out into the sun and into contact with the user, its temperature then possibly going from 20xc2x0 C. to 40xc2x0 C. In which case, the power supply voltage is not set optimally either.
An object of the present invention is thus to provide a better solution, tending better than the prior art solution towards optimum adjustment of the power supply voltage, so as to save energy, in order to increase the operating time of the apparatus between battery recharging or battery replacement, or in order to reduce battery costs.
According to the invention, electronic evaluation means are provided within the electronic circuit so as to deliver an indication of the operating conditions of the electronic circuit, which indication is used to adjust the power supply voltage to a minimum value at which said electronic circuit can still operate correctly.
In an embodiment of the invention, said electronic evaluation means comprise an oscillator whose operating frequency delivers said indication. This frequency is then converted into a signal of corresponding voltage which is compared with a reference value which is also a voltage, the result of said comparison being used to adjust the power supply voltage to a minimum value at which said electronic circuit can still operate correctly.
In another embodiment, said evaluation means comprise a test circuit comprising at least one circuit that is sensitive to the value of the power supply voltage and to the environmental conditions, the circuit periodically receiving one or more stimuli and delivering at least one test signal used to adjust the power supply voltage to a minimum value at which said electronic circuit can still operate correctly.
In yet another embodiment, said evaluation means comprise a device delivering an evaluation signal representing the temperature to which said electronic circuit is subjected, and a conversion device converting said evaluation signal into a control signal that is used to adjust the power supply voltage to a minimum value at which said electronic circuit can still operate correctly.